Обсуждение: Enforcing that all WAL has been replayed after restoring from backup
Currently, if you take a backup with "pg_basebackup -x" (which means it will include all the WAL to required restore within the backup dump), and hit Ctrl-C while the WAL is being streamed, you end up with a data directory that you can start postmaster from, even though the backup was not complete. So what appears to be a valid backup - it starts up fine - can actually be corrupt. I put in a check against that back in March, but it had to be reverted because it broke crash recovery when the system crashed while a pg_start_backup() based backup was in progress: http://archives.postgresql.org/message-id/4DA58686.1050501@enterprisedb.com Here's a patch to add it back in a more fine-grained fashion. The patch adds an extra line to backup_label, indicating whether the backup was taken with pg_start/stop_backup(), or by streaming (= pg_basebackup). For a backup taken with pg_start_backup(), the behavior is kept the same as it has been - if the end-of-backup record is not reached during crash recovery, the database starts up anyway. But for a streamed backup, you get an error at startup. I think this is a nice additional safeguard to have, making streamed backups more robust. I'd like to add this to 9.1, but it required an extra field to be added to the control file, so it would force an initdb. It's probably not worth that. Or, we could sneak in the extra boolean field to some currently unused pad space in the ControlFile struct. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
Вложения
Excerpts from Heikki Linnakangas's message of mar ago 09 05:00:00 -0400 2011: > I think this is a nice additional safeguard to have, making streamed > backups more robust. I'd like to add this to 9.1, but it required an > extra field to be added to the control file, so it would force an > initdb. It's probably not worth that. Or, we could sneak in the extra > boolean field to some currently unused pad space in the ControlFile struct. How about making the new backup_label field optional? If absent, assume current behavior. -- Álvaro Herrera <alvherre@commandprompt.com> The PostgreSQL Company - Command Prompt, Inc. PostgreSQL Replication, Consulting, Custom Development, 24x7 support
Re: Enforcing that all WAL has been replayed after restoring from backup
От
Heikki Linnakangas
Дата:
On 09.08.2011 18:20, Alvaro Herrera wrote: > Excerpts from Heikki Linnakangas's message of mar ago 09 05:00:00 -0400 2011: > >> I think this is a nice additional safeguard to have, making streamed >> backups more robust. I'd like to add this to 9.1, but it required an >> extra field to be added to the control file, so it would force an >> initdb. It's probably not worth that. Or, we could sneak in the extra >> boolean field to some currently unused pad space in the ControlFile struct. > > How about making the new backup_label field optional? If absent, assume > current behavior. That's how I actually did it in the patch. However, the problem wrt. requiring initdb is not the new field in backup_label, it's the new field in the control file. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> On 09.08.2011 18:20, Alvaro Herrera wrote:
>> How about making the new backup_label field optional? If absent, assume
>> current behavior.
> That's how I actually did it in the patch. However, the problem wrt.
> requiring initdb is not the new field in backup_label, it's the new
> field in the control file.
Yeah. I think it's too late to be fooling with pg_control for 9.1.
Just fix it in HEAD.
regards, tom lane
Re: Enforcing that all WAL has been replayed after restoring from backup
От
Heikki Linnakangas
Дата:
On 09.08.2011 19:07, Tom Lane wrote: > Heikki Linnakangas<heikki.linnakangas@enterprisedb.com> writes: >> On 09.08.2011 18:20, Alvaro Herrera wrote: >>> How about making the new backup_label field optional? If absent, assume >>> current behavior. > >> That's how I actually did it in the patch. However, the problem wrt. >> requiring initdb is not the new field in backup_label, it's the new >> field in the control file. > > Yeah. I think it's too late to be fooling with pg_control for 9.1. > Just fix it in HEAD. Done. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
On Tue, Aug 9, 2011 at 18:07, Tom Lane <tgl@sss.pgh.pa.us> wrote: > Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes: >> On 09.08.2011 18:20, Alvaro Herrera wrote: >>> How about making the new backup_label field optional? If absent, assume >>> current behavior. > >> That's how I actually did it in the patch. However, the problem wrt. >> requiring initdb is not the new field in backup_label, it's the new >> field in the control file. > > Yeah. I think it's too late to be fooling with pg_control for 9.1. > Just fix it in HEAD. Should we add a note to the documentation of pg_basebackup in 9.1 telling people to take care about the failure case? Or add a signal handler in the pg_basebackup client emitting a warning about it? -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/
Re: Enforcing that all WAL has been replayed after restoring from backup
От
Heikki Linnakangas
Дата:
On 10.08.2011 12:29, Magnus Hagander wrote: > On Tue, Aug 9, 2011 at 18:07, Tom Lane<tgl@sss.pgh.pa.us> wrote: >> Heikki Linnakangas<heikki.linnakangas@enterprisedb.com> writes: >>> On 09.08.2011 18:20, Alvaro Herrera wrote: >>>> How about making the new backup_label field optional? If absent, assume >>>> current behavior. >> >>> That's how I actually did it in the patch. However, the problem wrt. >>> requiring initdb is not the new field in backup_label, it's the new >>> field in the control file. >> >> Yeah. I think it's too late to be fooling with pg_control for 9.1. >> Just fix it in HEAD. > > Should we add a note to the documentation of pg_basebackup in 9.1 > telling people to take care about the failure case? Something like "Note: if you abort the backup before it's finished, the backup won't be valid" ? That seems pretty obvious to me, hardly worth documenting. > Or add a signal > handler in the pg_basebackup client emitting a warning about it? We don't have such a signal handler pg_dump either. I don't think we should add it. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
On Wed, Aug 10, 2011 at 12:44, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> wrote: > On 10.08.2011 12:29, Magnus Hagander wrote: >> >> On Tue, Aug 9, 2011 at 18:07, Tom Lane<tgl@sss.pgh.pa.us> wrote: >>> >>> Heikki Linnakangas<heikki.linnakangas@enterprisedb.com> writes: >>>> >>>> On 09.08.2011 18:20, Alvaro Herrera wrote: >>>>> >>>>> How about making the new backup_label field optional? If absent, >>>>> assume >>>>> current behavior. >>> >>>> That's how I actually did it in the patch. However, the problem wrt. >>>> requiring initdb is not the new field in backup_label, it's the new >>>> field in the control file. >>> >>> Yeah. I think it's too late to be fooling with pg_control for 9.1. >>> Just fix it in HEAD. >> >> Should we add a note to the documentation of pg_basebackup in 9.1 >> telling people to take care about the failure case? > > Something like "Note: if you abort the backup before it's finished, the > backup won't be valid" ? That seems pretty obvious to me, hardly worth > documenting. I meant something more along the line of that it looks ok, but may be corrupted. >> Or add a signal >> handler in the pg_basebackup client emitting a warning about it? > > We don't have such a signal handler pg_dump either. I don't think we should > add it. Hmm. I guess an aborted pg_dump will also "look ok but actually be corrupt" (or incomplete). Good point. -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/
On Wed, Aug 10, 2011 at 6:53 AM, Magnus Hagander <magnus@hagander.net> wrote: > On Wed, Aug 10, 2011 at 12:44, Heikki Linnakangas > <heikki.linnakangas@enterprisedb.com> wrote: >> On 10.08.2011 12:29, Magnus Hagander wrote: >>> >>> On Tue, Aug 9, 2011 at 18:07, Tom Lane<tgl@sss.pgh.pa.us> wrote: >>>> >>>> Heikki Linnakangas<heikki.linnakangas@enterprisedb.com> writes: >>>>> >>>>> On 09.08.2011 18:20, Alvaro Herrera wrote: >>>>>> >>>>>> How about making the new backup_label field optional? If absent, >>>>>> assume >>>>>> current behavior. >>>> >>>>> That's how I actually did it in the patch. However, the problem wrt. >>>>> requiring initdb is not the new field in backup_label, it's the new >>>>> field in the control file. >>>> >>>> Yeah. I think it's too late to be fooling with pg_control for 9.1. >>>> Just fix it in HEAD. >>> >>> Should we add a note to the documentation of pg_basebackup in 9.1 >>> telling people to take care about the failure case? >> >> Something like "Note: if you abort the backup before it's finished, the >> backup won't be valid" ? That seems pretty obvious to me, hardly worth >> documenting. > > I meant something more along the line of that it looks ok, but may be corrupted. Yeah. I'm frankly pretty nervous about shipping 9.1 with this problem, but note that I don't have a better idea. I'd favor making pg_basebackup emit a warning or maybe even remove the backup if it's aborted midway through. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
On Wed, Aug 10, 2011 at 1:19 PM, Robert Haas <robertmhaas@gmail.com> wrote: > On Wed, Aug 10, 2011 at 6:53 AM, Magnus Hagander <magnus@hagander.net> wrote: >> On Wed, Aug 10, 2011 at 12:44, Heikki Linnakangas >> <heikki.linnakangas@enterprisedb.com> wrote: >>> On 10.08.2011 12:29, Magnus Hagander wrote: >>>> >>>> On Tue, Aug 9, 2011 at 18:07, Tom Lane<tgl@sss.pgh.pa.us> wrote: >>>>> >>>>> Heikki Linnakangas<heikki.linnakangas@enterprisedb.com> writes: >>>>>> >>>>>> On 09.08.2011 18:20, Alvaro Herrera wrote: >>>>>>> >>>>>>> How about making the new backup_label field optional? If absent, >>>>>>> assume >>>>>>> current behavior. >>>>> >>>>>> That's how I actually did it in the patch. However, the problem wrt. >>>>>> requiring initdb is not the new field in backup_label, it's the new >>>>>> field in the control file. >>>>> >>>>> Yeah. I think it's too late to be fooling with pg_control for 9.1. >>>>> Just fix it in HEAD. >>>> >>>> Should we add a note to the documentation of pg_basebackup in 9.1 >>>> telling people to take care about the failure case? >>> >>> Something like "Note: if you abort the backup before it's finished, the >>> backup won't be valid" ? That seems pretty obvious to me, hardly worth >>> documenting. >> >> I meant something more along the line of that it looks ok, but may be corrupted. > > Yeah. I'm frankly pretty nervous about shipping 9.1 with this > problem, but note that I don't have a better idea. I'd favor making > pg_basebackup emit a warning or maybe even remove the backup if it's > aborted midway through. I don't understand why we need to change pg_control for this? Why can't we just add a line to backup_label as the first action of pg_basebackup and then updated it the last action to show the backup set is complete? That would be safe for 9.1 -- Simon Riggs http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services
Re: Enforcing that all WAL has been replayed after restoring from backup
От
Heikki Linnakangas
Дата:
On 10.08.2011 15:34, Simon Riggs wrote: > On Wed, Aug 10, 2011 at 1:19 PM, Robert Haas<robertmhaas@gmail.com> wrote: >> On Wed, Aug 10, 2011 at 6:53 AM, Magnus Hagander<magnus@hagander.net> wrote: >>> On Wed, Aug 10, 2011 at 12:44, Heikki Linnakangas >>> <heikki.linnakangas@enterprisedb.com> wrote: >>>> On 10.08.2011 12:29, Magnus Hagander wrote: >>>>> >>>>> On Tue, Aug 9, 2011 at 18:07, Tom Lane<tgl@sss.pgh.pa.us> wrote: >>>>>> >>>>>> Heikki Linnakangas<heikki.linnakangas@enterprisedb.com> writes: >>>>>>> >>>>>>> On 09.08.2011 18:20, Alvaro Herrera wrote: >>>>>>>> >>>>>>>> How about making the new backup_label field optional? If absent, >>>>>>>> assume >>>>>>>> current behavior. >>>>>> >>>>>>> That's how I actually did it in the patch. However, the problem wrt. >>>>>>> requiring initdb is not the new field in backup_label, it's the new >>>>>>> field in the control file. >>>>>> >>>>>> Yeah. I think it's too late to be fooling with pg_control for 9.1. >>>>>> Just fix it in HEAD. >>>>> >>>>> Should we add a note to the documentation of pg_basebackup in 9.1 >>>>> telling people to take care about the failure case? >>>> >>>> Something like "Note: if you abort the backup before it's finished, the >>>> backup won't be valid" ? That seems pretty obvious to me, hardly worth >>>> documenting. >>> >>> I meant something more along the line of that it looks ok, but may be corrupted. >> >> Yeah. I'm frankly pretty nervous about shipping 9.1 with this >> problem, but note that I don't have a better idea. I'd favor making >> pg_basebackup emit a warning or maybe even remove the backup if it's >> aborted midway through. > > I don't understand why we need to change pg_control for this? > > Why can't we just add a line to backup_label as the first action of > pg_basebackup and then updated it the last action to show the backup > set is complete? Hmm, that's not possible for the 'tar' output, but would work for 'dir' output. Another similar idea would be to withhold the control file in memory until the end of backup, and append it to the output as last. The backup can't be restored until the control file is written out. That won't protect from more complicated scenarios, like if you take the backup without the -x flag, and copy some but not all of the required WAL files manually to the pg_xlog directory. But it'd be much better than nothing for 9.1. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes:
> Hmm, that's not possible for the 'tar' output, but would work for 'dir'
> output. Another similar idea would be to withhold the control file in
> memory until the end of backup, and append it to the output as last. The
> backup can't be restored until the control file is written out.
> That won't protect from more complicated scenarios, like if you take the
> backup without the -x flag, and copy some but not all of the required
> WAL files manually to the pg_xlog directory. But it'd be much better
> than nothing for 9.1.
Maybe we're overcomplicating this. What about changing pg_basebackup to
print a message when the backup is completely sent/received? People
would get used to that quickly, and would know to be suspicious if they
didn't see it.
regards, tom lane
On Wed, Aug 10, 2011 at 1:45 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote: > Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes: >> Hmm, that's not possible for the 'tar' output, but would work for 'dir' >> output. Another similar idea would be to withhold the control file in >> memory until the end of backup, and append it to the output as last. The >> backup can't be restored until the control file is written out. > >> That won't protect from more complicated scenarios, like if you take the >> backup without the -x flag, and copy some but not all of the required >> WAL files manually to the pg_xlog directory. But it'd be much better >> than nothing for 9.1. > > Maybe we're overcomplicating this. What about changing pg_basebackup to > print a message when the backup is completely sent/received? People > would get used to that quickly, and would know to be suspicious if they > didn't see it. Yeah, but would they be sufficiently suspicious to think "oh, my backup is hopeless corrupted even if it seems to work"? I think a clearer warning is needed, at the very least, and if there's a way to prevent it altogether at least in straightforward cases, that would be even better. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company
On Wed, Aug 10, 2011 at 19:45, Tom Lane <tgl@sss.pgh.pa.us> wrote: > Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> writes: >> Hmm, that's not possible for the 'tar' output, but would work for 'dir' >> output. Another similar idea would be to withhold the control file in >> memory until the end of backup, and append it to the output as last. The >> backup can't be restored until the control file is written out. > >> That won't protect from more complicated scenarios, like if you take the >> backup without the -x flag, and copy some but not all of the required >> WAL files manually to the pg_xlog directory. But it'd be much better >> than nothing for 9.1. > > Maybe we're overcomplicating this. What about changing pg_basebackup to > print a message when the backup is completely sent/received? People > would get used to that quickly, and would know to be suspicious if they > didn't see it. That would suck for scripts, and have people redirect the output to /dev/null instead, wouldn't it? And it violates the "unix expectation" that is that a successful command will not write anything to it's output... -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/
Magnus Hagander <magnus@hagander.net> writes: >>> Or add a signal >>> handler in the pg_basebackup client emitting a warning about it? >> >> We don't have such a signal handler pg_dump either. I don't think we should >> add it. > > Hmm. I guess an aborted pg_dump will also "look ok but actually be > corrupt" (or incomplete). Good point. What about having the signal handler corrupt the backup by adding some garbage into it? Now the failure case is obvious… Regards, -- Dimitri Fontaine http://2ndQuadrant.fr PostgreSQL : Expertise, Formation et Support
On Thu, Aug 11, 2011 at 1:34 AM, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> wrote: > Hmm, that's not possible for the 'tar' output, but would work for 'dir' > output. Another similar idea would be to withhold the control file in memory > until the end of backup, and append it to the output as last. The backup > can't be restored until the control file is written out. > > That won't protect from more complicated scenarios, like if you take the > backup without the -x flag, and copy some but not all of the required WAL > files manually to the pg_xlog directory. But it'd be much better than > nothing for 9.1. We need to skip checking whether we've reached the end backup location only when the server crashes while base backup using pg_start_backup. Right? We can do this by *not* initializing ControlFile->backupStartPoint if the server is doing crash recovery and backupEndRequired is false. What about the attached patch? Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center
Вложения
Re: Enforcing that all WAL has been replayed after restoring from backup
От
Heikki Linnakangas
Дата:
On 16.08.2011 04:10, Fujii Masao wrote: > On Thu, Aug 11, 2011 at 1:34 AM, Heikki Linnakangas > <heikki.linnakangas@enterprisedb.com> wrote: >> Hmm, that's not possible for the 'tar' output, but would work for 'dir' >> output. Another similar idea would be to withhold the control file in memory >> until the end of backup, and append it to the output as last. The backup >> can't be restored until the control file is written out. >> >> That won't protect from more complicated scenarios, like if you take the >> backup without the -x flag, and copy some but not all of the required WAL >> files manually to the pg_xlog directory. But it'd be much better than >> nothing for 9.1. > > We need to skip checking whether we've reached the end backup location > only when the server crashes while base backup using pg_start_backup. Right? Yes. > We can do this by *not* initializing ControlFile->backupStartPoint if the server > is doing crash recovery and backupEndRequired is false. What about the attached > patch? Hmm, this behaves slightly differently, if you first try to start the restored server without recovery.conf, stop recovery, and restart it after adding recovery.conf. But I guess that's not a big deal, the check is simply skipped in that case, which is what always happens without this patch anyway. Committed this to 9.1, but kept master as it was. (sorry for the delay, I wanted to fix the bogus comment as soon as I saw it, but needed some time to ponder the rest of the patch) -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
On Wed, Aug 17, 2011 at 5:49 PM, Heikki Linnakangas <heikki.linnakangas@enterprisedb.com> wrote: > Hmm, this behaves slightly differently, if you first try to start the > restored server without recovery.conf, stop recovery, and restart it after > adding recovery.conf. But I guess that's not a big deal, the check is simply > skipped in that case, which is what always happens without this patch > anyway. Oh, I forgot to consider that case. Yeah, I agree with you. > Committed this to 9.1, Thanks a lot! > but kept master as it was. So, in master, we should change pg_controldata.c and pg_resetxlog.c for new pg_control field "backupEndRequired"? > (sorry for the delay, I wanted to fix the bogus comment as soon as I saw it, > but needed some time to ponder the rest of the patch) NM. Thanks! Regards, -- Fujii Masao NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center
Re: Enforcing that all WAL has been replayed after restoring from backup
От
Heikki Linnakangas
Дата:
On 17.08.2011 12:26, Fujii Masao wrote: > So, in master, we should change pg_controldata.c and pg_resetxlog.c for > new pg_control field "backupEndRequired"? Ah, good catch! Fixed. -- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com